Chlorinated pyridylacetylene compounds

ABSTRACT

Trichlorovinylaromatic compounds having the general formula Ar-(CCl=CCl2)hd p WHEREIN Ar is perchlorinated phenyl or PERCHLORINATED PYRIDYL AND P IS AN INTEGER OF 1 TO 3 ARE DEHALOGENATED AND REDUCED BY ELECTROLYSIS TO GIVE AN AROMATIC ACETYLENE COMPOUND HAVING THE GENERAL FORMULA Ar&#39;&#39;-(C*CH)p WHEREIN Ar&#39;&#39; is the original aromatic NUCLEUS OR THE ORIGINAL AROMATIC NUCLEUS CONTAINING FEWER CHLORINE ATOMS. Such compounds are useful to control rice blast.

United States Patent Seiber et al.

[ June 27, 1972 [54] CHLORINATED PYRIDYLACETYLENE COMPOUNDS [72]Inventors: James N. Seiber, Davis; Vernon D. Parker,

- Oakland, both of Calif.

[73] Assignee: The Dow Chemical Company, Midland, Mich.

[22] Filed: Jan. 21, 1970 21 Appl. No.: 4,157

[52] US. Cl ..260/290 HL, 260/290 V, 260/651 R,

I 260/650 R, 71/94, 71/126, 204/72 [51] Int. Cl. ..C07d 31/26 [58] Fieldof Search ..260/290 HL, 290 V [56] References Cited UNITED STATESPATENTS 3,045,022 7/1'962 McGill ..260/290V Primary Examiner-Henry R. Jiles Assistant Examiner-S. D. Winters Attorney-Griswold and Burdick,Herbert D. Knudsen and C. E. Rehberg 57 ABSTRACT Trichlorovinylaromaticcompounds having the general formula wherein Ar is perchlorinated phenylor perchlorinated pyridyl and p is an integer of l to 3 aredehalogenated and reduced by electrolysis to give an aro matic acetylenecompound having the general formula wherein Ar is the original aromaticnucleus or the original aromatic nucleus containing fewer chlorineatoms. Such compounds are useful to control rice blast.

5 Claims, No Drawings CHLORINATED PYRIDYLACETYLENE COMPOUNDS BACKGROUNDOF THE INVENTION Feoktistov and Tomilov in USSR Pat. No. 158,869 (1963)CA. 60, 1 1,894 (1964) show a method of preparing ethylene fromiodochloroethane and a method of preparing 2-chlorol,l-difluoroet hylenefrom l,l,l-trifluoro-2-chloro-2- bromoethane by means of anelectrochemical dehalogenation. Halogenated ethane was the onlysubstrate used in the patent and the product contained only ethylenicunsaturation.

Zinc has been used to prepare acetylenic compounds. Weis in Helv. Chim.Acta. 49, 234 (1965) describes a method for dehalogenating l l,2,2-tetrachlorol ,2-bis(4-chlorophenyl-)ethane by contacting thecompound with zinc in boiling dimethylformamide to formbis(4-chlorophenyl)acetylene. Finnegan and Norris in J. Org. Chem. 28, l139 (1963) show a method of preparing 3,3,3-trifluoropropyne by reacting'l ,l,2- trichloro-3,3,3-trifluoropropene with zinc dust in the presenceof a suitable solvent. The yield of the acetylenic compound varied from12 to 32 percent.

SUMMARY OF THE INVENTION The present invention is a new process and newchloropyridylacetylene compounds prepared by dehalogenating and reducingtrichlorovinylaromatic compounds having the general formula wherein Aris perchlorinated phenyl or perchlorinated pyridyl'and p is an integerof l to 3 by electrolysis to produce an aromatic acetylene compoundhaving the general formula Ar'(C 5 CH),

wherein Ar is the original aromatic nucleus, or the original aromaticnucleus containing fewer chlorine atoms.

The novel features of the present invention arethe newchloropyridylacetylenes and the utilization of an electrolysis reactionto convert a perchlorinated vinylaromatic compound to a correspondingaromatic acetylene compound. Although the aromatic compounds of theinvention may contain up to three' perchlorovinyl groups, thosecompounds containing only one such vinyl group, i.e. where p l in thegeneral formula, are preferred.

The new chloropyridylacetylenes produced in the present invention maysuitably contain 1 to 4 chlorines and l to 3 acetylene groups. Preferredchloropyridylacetylenes have only one acetylene group, with the isomersof tetrachloropyridylacetylenes being especially preferred.

The starting perchlorinated vinylaromatic 'materials of the presentinvention may be conveniently prepared by the high temperature, vaporphase chlorination of the corresponding ethyl-substituted aromaticcompound. For example, octachlorostyrene is prepared by the chlorinationof ethylbenzene at 600 C.

In the electrolytic reduction of compounds of the present invention,chlorines on the aromatic nucleus are removed if reduction is continuedbeyond'the removal of the halogens on the trichlorovinyl group. Thus,the original aromatic trichlorovinyl compound may be reduced to anaromatic acetylene compound having an aromatic nucleus with fewerchlorines than the original nucleus.

The concentration of the reactants in the electrolytic cell may varywidely as different reactants and solvents are employed in the reaction.As a general rule, reactant concentrations of about 0.01 to about 2moles per liter of cell liquid are preferred, with about 0.1 to about0.5 moles of reactant per liter of cell solution being especiallypreferred.

The design of the electrolysis cell used in the present invention is notcritical. Numerous electrolytic cells known in the art may be readilyemployed in the present invention. Preferred electrolytic cells havecathodes of mercury, lead, iron, tin or zinc, with lead and mercurybeing especially preferred. The anode may beessentially any chemicallyinert material with graphite and platinum being especially preferred.Such preferred cell may be arranged in any conventional design.

The electrolyte used in the present invention may vary widely. Preferredelectrolytes in the present invention are neutral salts, the salts ofweak or strong acids, the salts of a weak base and weak or strong acids.The use of strong bases may be detrimental to the progress of thereaction because of the tendency of such electrolytes to substitute forthe halogens. Specific examples of preferred electrolytes include sodiump-toluenesulfonate, sodium acetate, ammonium ptoluene-sulfonate,tetramethylammonium chloride, and hydrochloric acid, sulfuric acid,acetic acid or phosphoric acid used alone or in combination with ammoniaor a tertiary amine. Especially preferred is the use of ammoniumacetate, ammonium chloride or RG1 as an electrolyte. The concentrationof the electrolyte may vary widely as different ,electrolytes, currentdensities and cathode potentials are employed.

The solvent employed in the electrolysis solution may vary widely asdifferent reactants are employed in the electrolytic dehalogenation. Thesolvent should dissolve all or most of the starting material and theelectrolyte and should be inert under the electrolysis conditions.Solvents preferred in the present invention include the lower alcohols,dialkyl and alkylene ethers, lower alkylene glycol monoalkyl ethers anddialkyl ethers and lower amides. Representau've examples of thesepreferred solvents include: alcohols such as methanol, ethanol,isopropanol and isobutyl alcohol; dialkyl ethers and alkylene etherssuch as diethyl ether, dipropyl ether, dioxane and tetrahydrofuran;lower alkylene glycol monoalkyl ethers and dialkyl ethers such asZ-methoxy-propanol, ethoxyethanol, dimethoxyeth'ane andl,2-dimethoxypropane; and lower amides such as dimethyl-formarnide andacetamide. These solvents of the present invention may be used eitheralone or preferably with up to about 30 percent by weight of water toassure proper solubility of the electrolyte.

In the operation of the electrolysis cell, the cathode potential isusually maintained between 0.5 and 2.5 volts versus the standard calomelelectrode, with cathode potentials of 0.7 to 2.0 volts being especiallypreferred. The applied voltage provided by the power source may varywidely depending upon the IR drop of the reaction medium. The IR drop ispreferably minimized to prevent overheating of the reaction cell. Thecurrent density may preferably range from about 0.01-0.5 amp/in. ofelectrode with 0.05 to 0.15 amp/in. being especially preferred. Thetemperature of the electrolysis reaction may vary widely. Thetemperatures may be varied to maintain the liquid phase withtemperatures from about 0 to about 100 C. or more being preferred andtemperatures of about 40 to about 60 C. being especially preferred.

The cell is usually and most conveniently operated at less than 100percent conversion to minimize the over-reduction and dehalogenation ofthe product under the reaction conditions. As a general rule, 70 topercent of the reduction theoretically required gives the most favorableyields of the desired product.

After the electrolysis, the product may be isolated by diluting the cellliquor with water and cooling the precipitated product. During thecourse of the reaction, a high concentration of reactants and productsmay be maintained in the electrolytic cell so that the product iscrystallized from the cell liquor without the addition of water. Alsoafter the termination of the electrolysis reaction, the solvent of theelectrolytic cell may be distilled off, the crude product may be washedof inorganic salts and the product obtained by crystallization.

The acetylenic compounds prepared by the present invention have usefulbiological activity against rice blast; the triple bond may also bereduced to prepare the corresponding vinyl aromatic compounds which areuseful in preparing fire retardant polymers.

SPECIFIC EMBODIMENTS Example 1 An electrolysis cell was prepared usingalternating plates of sheet lead as the cathode and graphite as theanode so that the total working areas of the cathode and anode were 75square inches each. A saturated calomel reference electrode (SCE),magnetic stirring bar, thermometer and reflux condenser were also placedin the cell. When filled with solution, the electrolysis cell had atotal volume'of 2.5 liters. To this cell was added a solution of 70grams (0.185 mole) of octachloro-styrene in a mixture of 1 liter ofmethanol and 1.2 liters of dimethoxyethane containing 20 ml. ofconcentrated aqueous ammonia. Also added to the cell were 150 grams ofammonium acetate as the electrolyte and 100 ml. of water. Electrolysiswas conducted over a period of 2 hours applying a voltage of volts togive a cathode potential of l .2 volts vs. SCE and a current 1 densityof 0.15 amp. per square inch of electrode. During the course ofelectrolysis, the temperature rose to 60 C. The progress of the reactionwas followed by taking periodic samples of the cell solution andanalyzing them by vapor phase chromatography. The reaction wasterminated after a conversion of 86 percent had been obtained. Thecurrent efficiency at this point was 80 percent for a transfer of 4Faradays of electricity per mole of reactant. At the termination of theelectrolysis, the analysis of the product showedthat 13.6 percent wasoctachlorostyrene, 6.8 percent was1,2-dichloro-1-(pentachlorophenyl)ethylene, 60.3% waspentachlorophenylacetylene and 19.3 percent wastetrachlorophenylacetylene. The hot reaction solution was drained fromthe cell and 250 ml. of water was added. After standing overnight atroom temperature, buff-colored crystals formed. These crystals werecollected and dried to give 26.4 grams (52.3% yield) ofpentachlorophenylacetylene having a melting point of l802 C. [lit. m.p.185 to 186 C., J. 'Am. Chem. Soc. 83, 408 (1961)]. The product was alsoanalyzed by elemental analysis, nuclear magnetic resonance spectroscopyand infrared spectroscopy.

EXAMPLES 2-5 In the same manner as described in Example 1, 70 grams(0.185 mole) of octachlorostyrene was electrolyzed in four parallelexperiments in a solution of 100 ml. of water, 1 liter of methanol and1.2 liters of dimethoxyethane containing the electrolyte concentrationsshown in Table l. The cell was Yield, percent Eloc- Electrolyte,

Ex. trade molar solutions C5015 E CH CBHChC CH 2 Hg 1.0 NH OAe 34. 6 9.9

3 Pb 1.0 NH OAc, 69.8 22.4

4 Pb 0.5 NH C1 80. 2 2. 2

EXAMPLE 6 REDUCTION OF Z-TRICHLOROVINYL- 3 ,4,5,6-TETRACHLOROPYR1DINEtetrachloropiridine in 100 m1. of methanol and 120 ml. of drmethoxye anecontaining grams of ammonium acetate,

2 ml. of concentrated aqueous ammonia, and 10 ml. of water waselectrolyzed in the manner shown by the examples above. When analysis ofa sample by vapor phase chromatography indicated that 81% conversion hadbeen obtained, the electrolysis was terrninated and the reactionsolution was diluted with water and extracted with methylene chloride.Upon evaporation of the methylene chloride extract, 6.5 grams of a crudeoily solid wereobtained. The major product, 50.6 percent,

1 was identified as shown in Example 1 to be 3,4,5,6-

tetrachloropyridylacetylene which had a melting point of 108 to l 1 1 C.A secondary product, 13 percent, was identified astrans-l-chloro-2-(3,4,5,6-tetrachloropyridyl) ethylene and had a meltingpoint of 1 16 to 121 C.

EXAMPLE 7 REDUCTION OF 3-TRICHLOROV-INYL- 2,4,5 ,6-TETRACHLOROPYRIDINEIn the same-manner as described in Example 3, 8.0 grams (0.023 mole) of3-trichlorovinyl tetrachloro-pyridine was electrolyzed to give a crudeproduct at a conversion of 73 percent at a current efiiciency of 40percent. The major product, 50.7 percent, was identified in the samemanner as shown above to be 2,4,5,6-tetrachloropyridylacetylene,off-white crystals having a melting point of 85 to 88 C.

EXAMPLE 8 Rice plants were wetted with a 400 p.p.m. aqueous suspensionof pentachlorophenylacetylene. The treated plants and a standard werethen inoculated with rice blast. The plants were then stored inconditions suitable for infection and development of the disease. Afterthe disease was well developed, the treated plants were compared to anuntreated standard. The treatment with pentachlorophenylacetylene gave83 percent control of rice blast, whereas the standard showed nocontrol.

Also, any of the novel acetylenic compounds taught above may be used tocontrol rice blast as described in Example 8, for example,tetrach]oropyridylacetylenemay be applied to rice plants to control riceblast.

We claim:

1. A chloropyridylacetylene compound of the formula (:1x 0 (05cm where pis an integer of 1'3 and x is an integer of 1 to (S-p). 2. The compoundof claim 1 wherein p=l. 3. The compound of claim 1tetrachloropyridylacetylene.

4. The compound of claim 1 which is 3,4,5,6-'tetrachloropyridylacetylene.

5. The compound of claim 1 which is 2,4,5,6-tetrachloropyridylacetylene.

which is a

2. The compound of claim 1 wherein p
 1. 3. The compound of claim 1 whichis a tetrachloropyridylacetylene.
 4. The compound of claim 1 which is3,4,5,6-tetrachloropyridylacetylene.
 5. The compound of claim 1 which is2,4,5,6-tetrachloropyridylacetylene.